Significant advancements have been made in motor vehicle crash protection in recent decades. These improvements have been provided through numerous technologies. Particularly significant have been advancements in the area of occupant restraints. Occupant restraints can be divided into passive and active categories, with the most widely employed passive restraint system in the form of pyrotechnically inflated airbags. These devices can be used for frontal and side impact scenarios, as well as other crash conditions. Active restraint systems most commonly take the form of a manually fastened seatbelt restraint system. A combination of active and passive restraint systems, enhanced vehicle crashworthiness, and other features have led to safer vehicles.
Active type seatbelt systems in typical use in modern passenger motor vehicles are of the so-called three point variety. These systems include a lap belt portion which extends across the lower torso of the occupant and an upper or shoulder belt section passing diagonally across the upper torso of the occupant. The system is fastened and released using a single buckle. In order to provide enhanced comfort and convenience, and accommodate various operators and use conditions, seatbelt webbing retractors are provided. These devices stow a length of webbing on a rotationally biased spool that provides retraction and extraction of webbing. Active seatbelt systems are maintained in a stowed condition when the vehicle is unoccupied, and does not interfere with occupant ingress and egress. These belt systems are manually donned as the occupant fastens the belt to a buckle, extending the shoulder belt and lap belt sections across the occupant.
Today's three point belt systems may be of a type using a single belt retractor in which one end of the belt is anchored to the vehicle, and the other is affixed to the retractor spool. In such systems, a sliding latch plate or tongue is used which is slid along the webbing to provide an appropriate length of the lap and shoulder belt sections for a particular user. Another type in wide-spread use is a dual retractor system in which the tongue is affixed to two separate lengths of webbing, one of which provides the shoulder belt section and is coupled to a shoulder belt retractor, and another length of webbing provides the lap belt section and is coupled to a lap belt retractor.
Numerous additional components and systems have been developed and implemented to enhance the comfort and convenience, and occupant protection provided by belt restraint systems. For example, a host of retractor control systems are used to allow the occupant to extend and retract the webbing from the retractor during normal use, but which lock upon a detected vehicle deceleration, which is known as an emergency locking retractor function. Webbing pretensioners are provided to preload the belt restraint system by taking up webbing slack upon the detection of an actual or imminent vehicle impact. Many of the pretensioner systems are pyrotechnically activated and therefore may be fired only once, generally upon the detection of an actual vehicle impact. Categories of these devices include pyrotechnic lap pretensioners (PLP) which are typically linear stroke devices at the anchor side of a lap belt mounted to the seat or floor pan. Pyrotechnic buckle pretensioners (PBP) are also typically linear stroke devices and are mounted to the buckle of a three point belt system. Retractor pretensioners act on the retractor spool to cause rapid retraction of belt webbing. A new generation of retractors includes so-called pre-pretensioners which are typically electric motor driven and provide retraction of webbing upon the detection of an imminent vehicle impact and operate in a reversible manner.
The technology of controlling occupant kinematics during vehicle impacts has also undergone fundamental advancements. Automotive engineers seek to provide a high degree of control of the occupant kinematics during an impact over a variety of impact types and severities, as well as for different occupant classifications of size, weight, and occupant position. The degree of displacement or excursion of the occupant during impacts is managed in order to reduce belt loads and the severity of occupant impacts with other structures within the vehicle. Single retractor systems pose an additional design challenge. Since the belt tongue may slide along the belt webbing during an impact, belt forces may cause the webbing to move through the belt tongue and thereby change the effective lengths of the lap and shoulder belt sections. There is a desire to reduce this “load redistribution” between the lap and shoulder belt sections.
Even through the use of dual retractor systems, it is a challenge to provide a desired degree of control of excursion of the occupant's lower torso. Excessive excursion of the occupant's lower torso can result in high femur loads being applied as the occupant engages the vehicle instrument panel and adjacent structure during a frontal impact. Excessive lower torso excursion may also result in “submarining” in which the occupant partially slides under the lap belt section, which is undesirable. Furthermore, in order to reduce the severity of occupant injuries in dynamic events, there is a desire to decrease chest deflection which can be achieved by reducing shoulder belt loads. At the same time, reducing femur loads requires earlier coupling between the occupant and the lap belt.
In addition to continuously striving for enhanced occupant protection, automotive engineers further seek to reduce the complexity, weight and packaging volume requirements of automotive components as vehicles become more fuel efficient. Furthermore, when performance enhancements are provided for belt restraint systems, it is desirable to maintain the ease with which the system is donned and released.